According to documents released by Wikileaks and seen by The Telegraph, as recently as December 2008 an official from the International Atomic Energy Agency expressed concern that strong earthquakes posed a "serious problem" for nuclear plants, that safety rules were out of date.
The document states: "He [the IAEA official] explained that safety guides for seismic safety have only been revised three times in the last 35 years and that the IAEA is now re-examining them.
"Also, the presenter noted recent earthquakes in some cases have exceeded the design basis for some nuclear plants, and that this is a serious problem that is now driving seismic safety work."
The cables also disclose how the Japanese government opposed a court order to shut down another nuclear power plant in western Japan because of concerns it could not withstand powerful earthquakes.
I'm not going to opine much on this one, but take it for what it's worth. There's always a tension between regulators and the people being regulated--and it appears that Japan is no different than any other nation in this regard.
Here's the original cable, hosted by The Telegraph: 3-4 December Nuclear Safety and Security Group
More on the Japan Earthquake:
Millions Saved in Japan By Good Engineering and Government Building Codes
How the Japan Earthquake Shortened Earth's Day